1. Field of the Invention
The present invention relates to a photothermographic imaging material which forms an image by thermal development, and particularly to a photothermographic imaging material with high sensitivity and low photographic fog, which is excellent in image storage stability after the development. Further, the present invention relates to a photothermographic imaging material, and particularly to a photothermographic imaging material which is high density, is excellent in light radiated image storage stability and image storage stability at the time of storage with high temperature, wherein increase of photographic fog is small in silver color tone and with time, and which is excellent in film transport and environmental suitability.
2. Description of Related Art
In earlier technology, in the fields of medical care and print plate making, waste solutions involved in wet-type processing of image formation materials have been problematic in terms of working property, and recently reduction of processing waste solutions has been strongly desired in the light of environmental preservation and saving space.
Recently, photothermal photographic materials where no waste solution involved in wet-type processing is produced have been strongly desired in terms of environmental protection and working property in the fields of medical care and printing. Particularly, technology where clear black images with high resolution can be formed by thermal development, concerning photothermal photographic materials of the intended use for photographic technology has been commercialized and rapidly prevailed. Since these photothermal photographic materials are typically developed at a temperature of 80° C. or above, they are referred to as photothermographic imaging materials in distinction from photosensitive materials in earlier technology which are liquid-developed at the range of 25 to 45° C. Thus, the photothermographic imaging materials where image formation can be performed only by adding heat have come into practical use and rapidly prevailed in the above fields.
In earlier technology, this type of the photothermographic imaging material is made up of a photosensitive layer comprising highly sensitive silver halide particles spectrally sensitized with dyes, an organic silver salt and a reducing agent, an irradiation prevention layer (AI layer) which prevents that light irradiated to the photosensitive layer is not absorbed, passes through, and reflects diffusely on an interface, an intermediate layer and an adhesion layer of a support or a backing layer (BC layer) provided at an opposite site of the support. Additionally, a protection layer is provided on the photosensitive layer and BC layer to prevent scratch at handling.
Since generally, in the photothermographic imaging material, the image is formed only by thermal development after exposure, the processing is simple, but since there is no photographic fixing step, it becomes important to improve image storage stability after the development. To improve the image storage stability after the development, the image could be generated by the development at high temperature, but if the development temperature is excessively high, photographic fog is easily produced and the sensitivity is reduced. Thus, generally, the development is performed at the temperature around 120±10° C.
The use of mercapto compounds to reduce the photographic fog is disclosed, for example, in JP-A-63-301037, JP-A-5-341432, JP-T-5-509182 and JP-A-2000-19681 or the like.
However, in these mercapto compounds, all have less effect on inhibition of the photographic fog, high sensitivity cannot be obtained, and there has been a limit to improve the image storage stability after the development.
Further, the use of certain propenenitrile compounds as photographic fog inhibitors is disclosed (e.g., see JP-T-2000-515995), and also the use of the certain alkene compound is disclosed (e.g., see JP-A-2002-207273). However, improvement effects of the image storage stability after the development have not been still sufficient in these compounds.
Further, it is disclosed that the use of the certain bisphenol compounds affords the good image in color tone (e.g., see JP-A-2002-169249), but these compounds have not been sufficient to improve the image storage stability after the development.
Since polyhalomethane compounds can release halogen radicals by photo or thermal excitation to reduce the photographic fog, they are proposed as inhibitors of the photographic fog of the photothermographic imaging materials. Examples thereof can include U.S. Pat. No. 3,874,946, U.S. Pat. No. 4,452,885, U.S. Pat. No. 4,546,075, U.S. Pat. No. 4,756,999, U.S. Pat. No. 5,340,712, JP-B-54-165, JP-A-50-137126, JP-A-7-2781, JP-A-9-265150 and JP-B-2-32614.
Various chemical structures for the groups which bind to polyhalomethane group have been designed in order to enhance releasing effects of halogen, but it can not be said yet that sufficient performance has been obtained. Because the sensitivity is often reduced when releasing ability of halogen is high whereas it becomes difficult to inhibit the photographic fog and it becomes difficult to improve the image storage stability when the releasing ability of halogen is small.
The photothermographic imaging material (hereinafter, simply also referred to as a photothermographic material or imaging material) per se has been already proposed since a long time ago (see, e.g., U.S. Pat. No. 3,152,904 Specification; U.S. Pat. No. 3,457,075 Specification; D. Morgan; Dry Silver Photographic Material; D. H. Klosterboer; Thermally Processed Silver System; Imaging Processes and Materials Neblette, 8th revision, Sturge, V. Walworth, A. Shepp edited, 279 page, 1989).
This photothermographic material is processed by a thermal development apparatus which adds stable heat to the photothermographic material to form the image, typically called a thermal developing apparatus. As mentioned above, in conjunction with the recent rapid prevalence, this thermal development apparatus has been supplied in the market in large quantities. In the meanwhile, there has been problematic in that slipping property between the photosensitive material and a transport roller or processing members of the thermal development apparatus changes, and transport failure and density unevenness occur. Also there has been problematic in that the density of the photothermographic imaging material varies with time. It has been found that these phenomena noticeably occur in the photothermographic imaging materials where image exposure is performed by laser light and subsequently the image is formed by thermal development. Further, recently, compaction of laser imager and acceleration of photographic processing have been required.
Therefore, property improvement of the photothermographic imaging material becomes essential. For the compaction of the thermal development apparatus, it is more advantageous to use a heat drum manner than to use a horizontal transport manner, but there has been problematic in that powder drop-off, density unevenness and roller mark easily occur. Further, even when the rapid processing is carried out, to obtain sufficient density of the photothermographic imaging material, it is effective to use those with small average particle size as silver halide to increase covering power or to use a high contrast agent such as hydrazine compounds and vinyl compounds (see, e.g., JP-A-11-295844 and JP-A-11-352627). However, when these technologies are used, trouble matters have occurred where density change with time after the thermal development (print out property) becomes large and the density unevenness at the thermal development deteriorates. Also, it is possible to improve the print out property by reducing an amount of a reducing agent or by reducing the amount of coated silver, but the trouble matter has occurred where the image density is decreased with time. Further, the trouble matter has occurred where silver color tone become greatly different from that of conventional wet-type X-ray film due to making silver halide fine particles. Disclosed are improving technology for the print out property (see, e.g., JP-A-2001-133925), modulation technology for the silver color tone (see, e.g., JP-A-2002-169249 and JP-A-2002-236334), and the technology where the increase of the photographic fog is inhibited at undeveloped states and during storage after the development (see, e.g., U.S. Pat. No. 5,686,228 Specification, U.S. Pat. No. 6,171,767 Specification and JP-A-2002-236335). But it could not say that they are sufficient to solve the above trouble matters.